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The purpose of this study was to evaluate the overall performance of rapid antigen detection (RAD) in group A streptococcus (GAS) in Finland by using the results of external quality assurance (EQA) samples. We also compared the performance of laboratory professionals to that of nursing professionals. Around 22,800 EQA results among a total of 383 laboratories and physician’s offices were analysed. Vocational data on the personnel who carried out the tests were available for 10,088 EQA samples, 7,428 of which were tested by laboratory technicians and 2,531 by nursing staff. The best overall performance was found with GAS-negative samples: 99% of the reports were correct. In contrast, the overall performance was only 76% when the samples were weakly positive for GAS antigen. The laboratory technicians performed statistically significantly better than the nursing staff, with both strongly positive (correct results 98.9% vs. 95.1%, respectively; p<0.001) and weakly positive (79.3% vs. 65.3%, respectively; p<0.001) samples. With negative samples, no difference in performance between the laboratory and nursing staff was found (99.5% vs. 99.0%, respectively). The professional skills of the person performing the RAD test for GAS have a major impact on the sensitivity of the test. Based on the results of this study, we suggest that EQA-like artificial specimens could be used as a tool to improve and validate the quality of RAD testing in individual testing sites. [ABSTRACT FROM AUTHOR]